STUDY ON THE SEISMIC BEHAVIOUR OF LOW-RISE OPEN GROUND STOREY FRAMED BUILDING

Due to increasing population since the past few years car parking space for residential apartments in populated cities is a matter of major concern. Hence the trend has been to utilize the first storey of the building itself for parking. These types of buildings having no infill masonry walls in first storey, but infilled in all upper storeys, are called Open First Storey (OFS) buildings. There is significant advantage of these category of buildings functionally but from a seismic performance point of view such buildings are considered to have increased vulnerability. From the past earthquakes it was evident that the major type of failure that occurred in OFS buildings included snapping of lateral ties, crushing of core concrete, buckling of longitudinal reinforcement bars etc. Due to the presence of infill walls in the entire upper storey except for the first storey makes the upper storeys much stiffer than the open first storey. Thus, the upper storeys move almost together as a single block, and most of the horizontal displacement of the building occurs in the soft first storey itself. In other words, this type of buildings sway back and forth like inverted pendulum during earthquake shaking, and hence the columns in the first storey columns and beams are heavily stressed. Therefore it is required that the first storey columns must have sufficient strength and adequate ductility. The vulnerability of this type of building is attributed to the sudden lowering of lateral stiffness and strength in first storey, compared to upper storeys with infill walls.